1. Field of the Invention
The present invention relates to a control valve for a variable displacement compressor, particular to a displacement control valve for a swash-plate-type variable displacement compressor which is applied to an on-vehicle air-conditioning unit or the like. The compressor has a devise for releasing a pressure in a crank chamber.
2. Related Art
Known displacement control valves for a swash-plate-type variable displacement compressor are disclosed in Japan patent Laid-open No. H. 3-53474, Japan Utility Model Laid-open No. H. 6-17010, and Japan patent Application Laid-open No. H. 8-177735.
The swash-plate-type variable displacement compressor having the control valve basically decreases in discharge displacement with increase of a crank chamber pressure of the compressor and increases in the displacement with the decrease of the crank chamber pressure.
The control valve opens and closes a communication passage communicating a suction port of the compressor with the crank chamber by using a valve element moving in response to a suction pressure of the compressor, thereby controlling the pressure of the crank chamber.
Furthermore, the valve element of the control valve is moved toward the open position by the discharge pressure of the compressor or by increasing a spring force of a correction spring resiliently biasing the valve element toward the open position with increase of the discharge pressure to vary the opening-closing switching point of the valve element in response to the discharge pressure. Thus, the control valve controls the discharge displacement in relation to an outer-air condition (or the discharge pressure).
Each known displacement control valve is constructed to achieve its object. However, a recent variable displacement compressor has a less leak flow rate of a fluid leaking into a crank chamber with regard to a discharge fluid in a piston/cylinder section. Thus, when the compressor provides a low discharge pressure, the crank chamber can not obtain an enough pressure for achieving a desired control performance as the displacement control valve, in which the control valve will not meet the compressor in their control performances.
Increase of the leak rate of a discharge pressure fluid leaking into the crank chamber would solve the problem in a low discharge pressure state of the compressor. However, this increases a pressure loss in a high discharge pressure state of the compressor, undesirably increasing a energy loss against an energy saving trend.
In view of the above-described disadvantage, an object of the invention is to provide an improved control valve for a swash-plate-type variable displacement compressor having a devise for releasing a pressure of a crank chamber. The improved control valve will not increase a pressure loss in a high discharge pressure state of the compressor and provides a solution of the problem in a low discharge pressure state of the compressor so as to have a control characteristic to meet with the performance of the compressor, enabling a displacement control in relation to an environmental condition.
For achieving the object, a first aspect of the invention is a control valve for variable displacement compressor which includes:
a valve housing having a communication passage communicating a suction port of the compressor with an crank chamber of the compressor,
a main valve provided in the valve housing for opening and closing the communication passage,
a spring member correction biasing the main valve toward its closed position, and
a pressure actuated unit for moving the main valve toward its open position by receiving a suction pressure of the compressor,
a flow adjustment valve disposed in the valve housing for adjusting an open degree of said leak passage and receiving the discharge pressure exerting a force on the leak flow adjustment valve toward its closed position, the leak flow adjustment valve increasing a leak flow rate of a fluid flowing from a discharge port of the compressor to a crank chamber through the leak flow adjustment valve when the compressor provides a lower discharge pressure, and
a correction spring disposed between the main valve and the leak flow adjustment valve, the correction spring resiliently biasing a valve element of the main valve toward the open position, the correction spring increasing in spring force with transfer of a valve element of the leak flow adjustment valve toward the closed position.
The flow adjustment valve may be a slide valve slidingly received in a valve receiving recess formed in the valve housing and defines a leak passage between an outer surface of the leak flow adjustment valve and an inner surface the valve receiving recess, the leak passage becoming shorter with the transfer of the valve element of the leak flow adjustment valve toward its open position, adjusting a leak flow rate of a fluid flowing from the compressor discharge port to the crank chamber.
A second aspect of the invention is a control valve for variable displacement compressor comprising:
a valve housing having a communication passage communicating a suction port of the compressor with a crank chamber of the compressor,
a main valve provided in the valve housing for opening and closing the communication passage,
a spring member resiliently biasing the main valve toward its closed position, and
a pressure actuated unit for moving the main valve toward its open position by receiving a suction pressure of the compressor,
an auxiliary biasing unit disposed in the valve housing and exerting a force on the main valve toward its valve open position by a differential pressure between a discharge pressure of the compressor and a pressure of the crank chamber,
a leak passage provided in said valve housing for communicating a discharge port of said compressor with said crank chamber, and
a leak flow adjustment valve disposed in the valve housing for adjusting an open degree of said leak passage and receiving a discharge pressure exerting a force on the leak flow adjustment valve toward the closed position, the leak flow adjustment valve increasing a leak flow rate of a fluid flowing from a discharge port of the compressor to a crank chamber through the leak flow adjustment valve when the compressor provides a lower discharge pressure.
The leak flow adjustment valve may be a variable flow orifice valve adjusting a leak flow rate of a fluid flowing from the discharge port of the compressor to the crank chamber, the flow rate being proportional to an open rate of the leak flow adjustment valve. Alternatively, the leak flow adjustment valve may be a check valve being open when the discharge pressure of the compressor is lower than a reference pressure.
Next, an operation of each invention aspect will be discussed.
In the control valve for variable displacement compressor of the first aspect of the invention, the main valve opens and closes the communication passage in response to the suction pressure of the compressor to control the crank chamber pressure. The valve element of the leak flow adjustment valve moves toward the valve closed potion with increase of a discharge pressure, which increases the spring force of the correction spring with increase of the discharge pressure. That is, the main valve varies in its open or close starting point in response to the discharge pressure, enabling a displacement control in relation to a load according to an environmental air condition (or in relation to the discharge pressure).
Furthermore, in a lower discharge pressure state of the compressor, the leak flow adjustment valve increases a leak rate of a fluid flowing from the discharge port to the crank chamber to increase the crank chamber pressure, thereby keeping a control characteristic of the displacement control valve when the compressor is providing a low discharge pressure. The control valve characteristic readily meets the performance of the compressor.
The leak flow rate of the fluid leaking from the compressor discharge port to the crank chamber is adjusted basically proportionally to the open degree of the leak adjustment valve, adjusting the crank chamber pressure in response to the discharge pressure.
In the control valve for the variable displacement compressor of the second aspect of the invention, the main valve opens and closes the communication passage in response to the suction pressure of the compressor to control the crank chamber pressure. The force exerted on the main valve by the auxiliary biasing unit increases with increase of the discharge pressure. That is, the main valve varies in its open or close starting point in response to the discharge pressure, enabling a displacement control in relation to the discharge pressure (a load according to an environmental air condition). Furthermore, in a lower discharge pressure state of the compressor, the leak flow adjustment valve increases the rate of a leak flowing from the discharge port to the crank chamber to increase the crank chamber pressure, thereby keeping a control characteristic of the displacement control valve when the compressor is providing a low discharge pressure. The control valve characteristic readily meets the performance of the compressor.
The leak rate of the fluid leaking from the compressor discharge port to the crank chamber is adjusted proportionally to the open degree of the orifice-type leak adjustment valve. This adjusts the crank chamber pressure according to the discharge pressure.
The check valve used for the leak adjustment valve opens to adjust the crank chamber pressure when the deferential pressure between the discharge pressure and the crank chamber pressure is smaller than the reference pressure.